The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2002-273692 filed Sep. 19, 2002, which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to an actuator having coils and magnets.
2. Description of the Related Art
In general, actuators are such that a second member is moved relative to a first member. With this movement, it is possible to move a sample or the like that is fixed to the second member or to give a haptic feel to a person""s fingertip that touches the second member. Various driving mechanisms have been proposed for such actuators.
Among those actuators, actuators having coils and magnets utilize the phenomenon that when a current flows through a coil existing in a magnetic field around a magnet, an electromagnetic force acts on the coil. A second member to which a coil is fixed is moved relative to a first member to which a magnet is fixed. These actuators are worth paying attention to particularly in that the second member can move two-dimensionally in a plane.
An information receiving and feel providing device disclosed in JP-A-2000-330688 is known as a device using such an actuator. This device has a configuration that a flat, two-dimensional actuator is mounted on a mouse, and provides haptic feel information in link with a picture on a personal computer. The actuator is configured in such a manner that magnets are fixed on a base, a coil holder that holds coils is placed over the magnets, and the four sides of the coil holder are supported by elastic members from outside.
Where an actuator as described above is used being incorporated in a small device such as a mouse, size increase of the mouse causes deterioration in its operability. To prevent the size increase of the mouse, it is necessary to reduce the size of the actuator so that it can be incorporated inside an ordinary mouse.
On the other hand, where a haptic feel is to be provided by using an actuator that is incorporated in a mouse, the haptic feel providing ability can be increased by increasing the thrust on the second member. For example, the thrust on the second member can be increased by increasing the strength of magnetic fields to be exerted on the coils by increasing the dimensions of the magnets. However, increasing the dimensions of the magnets causes size increase of the actuator, which is not favorable.
The present invention has been made to solve the above problem, and an object of the invention is to provide an actuator that can increase thrusts and can be reduced in size.
To attain the above object, an actuator according to the invention comprises a generally flat-plate-like first yoke plate; a generally flat-plate-like second yoke plate provided approximately parallel with the first yoke plate; a plurality of magnets fixed to a surface of the first yoke plate that is opposed to the second yoke plate; a plurality of coils provided parallel with a surface of the second yoke plate that is opposed to the first yoke plate; and a coil fixing member to which the coils are fixed to form a unitary body together.
Since the second yoke plate is provided approximately parallel with the first yoke plate, magnetic fluxes extending from the magnets on the first yoke plate are attracted by the second yoke plate. Therefore, the ratios of the Z component (i.e., the component in the direction in which a magnetic flux located close to the center of the pole surface of a magnet extends) of a magnetic flux to its X and Y components (i.e., the components parallel with the XY-plane) are small. As a result, the ratio of the Z component of an electromagnetic force acting on the wire of each coil to its X or Y component is small. That is, the magnetic fluxes efficiently act on the coils to be moved in the X and Y direction. As a result, the thrusts per unit magnetic flux, that is, the thrusts per unit magnet area, are increased. Therefore, the thrusts on the coils and the coil fixing member can be increased and the actuator can be miniaturized.
Since the ratio of the Z component of an electromagnetic force acting on the wire of each coil to its X or Y component is small, the inclination of the coils and the coil fixing member is suppressed. Further, the resistance between the coils and the coil fixing member and other members is reduced, whereby the coils and the coil fixing member can be moved stably.
Since the first yoke plate and the second yoke plate are provided, magnetic fluxes extending from the magnets are attracted by or go through the yoke plates. This makes it possible to suppress leakage of a magnetic flux outside the actuator.
The actuator may be such that the interval d1 between the magnets and the coils is longer than the interval d2 between the second yoke plate and the coils. Where the relationship d1 greater than d2 is established between the intervals d1 and d2, in the vicinity of the edge of a certain magnet, although the magnetic flux extending direction deviates from the Z direction, the ratios of the X and Y components of the magnetic flux to its Z component are small at the position of the part of the wire of a corresponding coil because that part of the wire is distant from the magnet concerned in the Z direction. As a result, the ratio of the Z component of an electromagnetic force acting on that part of the wire of the coil to its X or Y component is small, and hence the inclination of the coils and the coil fixing member can be suppressed even if the coils and the coil fixing member are moved relative to the first yoke plate in a wide range in the XY-plane. The resistance between the coils and the coil fixing member and other members is lowered, whereby the coils and the coil fixing member are allowed to move stably.
Alternatively, the actuator may be such that the interval d1 between the magnets and the coils is shorter than or equal to the interval d2 between the second yoke plate and the coils. Magnetic flux densities near the respective magnets increases as the interval between the magnets and the coils and the coil fixing member decreases. Therefore, establishing the relationship d1xe2x89xa6d2 between the intervals d1 and d2 makes it possible to further increase the thrusts on the coils and the coil fixing member.
The actuator may further comprise a magnetic member provided adjacent to the boundary of each adjoining pair of magnets among the plurality of magnets. In this case, in the vicinity of the edge of a certain magnet, although the magnetic flux extending direction deviates from the Z direction, a large part of a magnetic flux close to the joining portion of the two adjoining magnets goes through the magnetic member existing there. As a result, in the space between the magnets and the coils, the ratios of the X and Y components of the magnetic flux to its Z component are small and the ratio of the Z component of an electromagnetic force acting on part of the wire of a corresponding coil to its X or Y component is small. Therefore, the inclination of the coils and the coil fixing member can be suppressed even if the coils and the coil fixing member are moved relative to the first yoke plate in a wide range in the XY-plane. The frictional resistance between the coils and the coil fixing member and other members is reduced, whereby the coils and the coil fixing member can be moved stably.
The actuator may be such that one or both of the first yoke plate and the second yoke plate are formed with an opening, and that the coil fixing member has a pillar portion that is provided in a region facing the opening so as to penetrate through the opening and whose external size is larger than the internal size of the opening. Since this structure restricts the movable range of the coils and the coil fixing member, it is not necessary to provide separate members for restricting the movable range of the coils and the coil fixing member and hence the actuator can be miniaturized.
The actuator may be such that the second yoke plate is formed with the opening. This makes it unnecessary to form an opening in the first yoke plate. Since the sizes of the magnets provided on the first yoke plate can be kept unchanged, the formation of the opening does not influence the thrusts on the coils and the coil fixing member.
The actuator may further comprise a buffer member that is provided at the edge of the opening to contact the pillar portion or a portion of the pillar portion to contact the edge of the opening. This makes it possible to reduce impact that may occur when the pillar portion contacts the edge of the opening.
The actuator may be such that the coil fixing member has a pillar portion provided on one or both of the side facing the first yoke plate and the side facing the second yoke plate, and that the actuator further comprises a surrounding member whose outer size is larger than the outer size of the pillar portion and that is provided so as to surround the pillar portion. Since the surrounding member restricts the movable range of the coils and the coil fixing member, it is not necessary to provide separate members for restricting the movable range of the coils and the coil fixing member and hence the actuator can be miniaturized.
The actuator may be such that one or both of the first yoke plate and the second yoke plate are formed with an opening, and that the surrounding member is provided adjacent to the opening. Since the surrounding member can surround the pillar portion properly, the movable range of the coils and the coil fixing member can be restricted and the actuator can be minimized.
The actuator may further comprise a buffer member that is provided at a portion of the surrounding member to contact the pillar portion or a portion of the pillar portion to contact the surrounding member. This makes it possible to reduce impact that may occur when the pillar portion contacts the surrounding member.
The actuator may further comprise a restricting member provided in a fixed manner between the first yoke plate and the second yoke plate, for restricting the movable range of the coil fixing member. Since the restricting member restricts the movable range of the coils and the coil fixing member, it is not necessary to provide separate members for restricting the movable range of the coils and the coil fixing member and hence the actuator can be miniaturized.
The actuator may further comprise a buffer member that is provided at a portion of the restricting member to contact the coil fixing member or at a portion of the coil fixing member to contact the restricting member. This makes it possible to reduce impact that may occur when the coil fixing member contacts the restricting member.
The actuator may be such that one or both of the first yoke plate and the second yoke plate are formed with an opening, that the coil fixing member has a pillar portion that is provided in a region facing the opening so as to penetrate through the opening and whose external size is larger than the internal size of the opening, and that the actuator further comprises a haptic feel providing member that is fixed to the pillar portion so as to be located on the side of the opening opposite to the coil fixing member. This makes it possible to provide haptic information to a fingertip or the like that touches the haptic feel providing member.
The actuator may further comprise position detecting means for detecting a position of the coil fixing member relative to one of the first yoke plate and the second yoke plate. In the actuator having such position detecting means, a position of the coil fixing member relative to the first or second yoke plate. This makes it possible to control the movement of the coil fixing member by controlling the currents to flow through the coils on the basis of the detected relative position.